Carnitine (vitamin BT; 3-hydroxy-4-trimethylammonio-butanoate) is a quaternary ammonium compound biosynthesized from the amino acids lysine and methionine. In living cells, it is required for the transport of fatty acids from the cytosol into the mitochondria during the breakdown of lipids for the generation of metabolic energy. Carnitine exists in two stereoisomers. The biologically active form is L-carnitine, whilst its enantiomer, D-carnitine, is biologically inactive. Pure L-carnitine can be obtained by microbiological processes or by organic synthesis with subsequent purification steps.
Due to its vitamin-like function, L-carnitine has a broad range of pharmaceutical, food and cosmetic applications. L-carnitine is known to have positive effects on energy metabolism and the cardiovascular, muscular and nervous system of humans and animals. L-carnitine is also useful for other purposes, for instance as a nutrient for yeast and bacteria growth. Carnitine can be administered orally to humans and animals.
Solid L-carnitine has a high hygroscopy. Thus powder mixtures have a low stability, in particular storability, and are only of limited use in industry, especially in the food industry.
Various attempts have been made in the art to overcome the problem of hygroscopy. In order to reduce the hygroscopy, EP 0434088 B1 suggests using a salt of L-carnitine with L-tartric acid in the preparation of tablets or capsules.
US 2009/0082449 discloses methods for obtaining carnitine powders or granulates. The carnitine is coated on a solid carrier in order to obtain a coated granulate. In a first method, it is suggested to coat the solid carrier with an aqueous carnitine solution by preparing an aqueous suspension and spray-drying. However, a spray-drying process requires large amounts of water in the spray-drying solution. This is problematic, because the water has to be evaporated subsequently, which requires a large amount of energy and also time. In a second method, it is suggested to mix solid carnitine with a solid carrier. In a third method, a liquid solution of a starting material comprising a low amount of carnitine, such as a permeate or a fermentation product, is mixed with a carrier and subjected to a drying process in order to obtain a granulate. Again, relatively large amounts of water have to be used which subsequently have to be removed in an energy and time consuming process. As outlined in section [0093], the granules tend to form agglomerated particles.
A method for producing granulates coated with carnitine chloride is disclosed in JP 08-012569. According to this method, aqueous solutions comprising usually 30 to 60% by weight carnitine chloride are admixed with carriers which are preferably silica carriers. After drying, the product can be admixed with organic binders and pressed into tablets and the like.
However, the methods known in the art have various drawbacks. At first, removing high amounts of water from a granulate is time and energy consuming. Further, granulates produced by methods in the art usually have a limited flowability. The decrease in flowability over time is indicative of hygroscopy of the carnitine. The flowability of a granulate and the maintenance of the flowability over an extended time period are important product properties. A good flowability is important for handling a granulate, for instance when packaging and proportioning the granulate. Granulates of low flowability tend to stick to surfaces, such as interior surfaces of containers and devices. This is problematic when a granulate is packed and proportioned by mechanical devices. Even further, the hygroscopy is problematic when carnitine or a carnitine granulate is admixed with other components, as for example in feed products for animals. In food products, feed products or feed and food additives, the carnitine is often admixed with other nutrients or other feed or food additives. Due to the hygroscopy of the carnitine, reduced flowability and caking is observed in such mixtures.